Diversity receiving system



Aug. 18, 1942. R. E. SCHOCK DIVERSITY RECEIVING SYSTEM Filed April 30,1941 '3 Sheets-Sheet 1 TO U T/L/ZA T/ON 05 VIC E Sc. 6. POTENTIAL 56. G.POTENTIAL INVENTOR ROBERT E. SCI-IOCK ATTORNEY qvfiznfimm w m @3253 w mm m-+v i Mia a 0 m. .Y NM Q m Mm NE R T m .u n. wk T H l l n l v w ll YQv h wmw R B F m H -m m m q m MW J I R W I w :v mm %m Q m: fizm mwuw w vwtzm mdum MN E235 mi mi a K v 3 M v E2213 Y W i j I b W NN Aug. 18,1942.

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DIVERSITY RECEIVING SYSTEM Filed April 30, 1941 5 Sheets-Sheet 3 V gmanT0 UTILIZATION DEV/C(E Ffg. 3

Patented Aug. 18, 1942 UNITED DIVERSITY RECEIVING SYSTEM Robert E.Schock, Riverhead, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application April 30, 1941, Serial No. 391,055

8 Claims.

This invention relates to radio reception and more particularly to adiversity receiving system in which, in connection with several signalreceiving circuit arrangements, means are provided for avoiding thecancellation of the signals when they are combined out of phase.

In radio signalling, and particularly in connection with short wavereception, the phenomenon known as fading results in considerablevariation in the volume and quality of the signal from time to time. Itis well known in the art that if a simple combination of two signals ofa diversity system is adopted, there will be intervals when the signalswill be out of phase and will cancel. It has heretofore been proposed toovercome this difficulty by providing several receivers each associatedwith separate antennae so arranged with respect to each other that theeffect of fading will be different upon difierent receivers, means beingprovided to select from time to time the receiver which delivers thestrongest signal.

In accordance with the present invention, however, it is possible toavoid cancellation of the signals when they arrive out of phase in thedifferent channels. One of these channels is arranged to be blockedduring out of phase periods. Another method which may be employed,however, according to my invention is that which provides reversal ofthe phase of the incoming signals in one of two channels of a diversityreceiving system so that an in-phase combination of energies from thetwo channels may be obtained.

A principal object of my invention is to provide a simple circuitarrangement for a diversity receiving system in which, when signals arereceived out of phase by two separate antennae, the energy delivered byone of these antennae may be suppressed so as to avoid cancellation ofthe energy received by the other antenna.

Another object of my invention is to provide means in a diversityreceiving system for avoiding the out-of-phase cancellation of effectsof energy received on three or more separate antenna circuits.

It is still another object of my invention to provide means in adiversity receiving system for reversing the phase of energy collectedby a single antenna and making an in-phase combination of this energywith energy derived from one or more other antennae upon which receptionmay from time to time be out of phase with the .first said antenna.

The invention will now be described in more detail, reference being madeto the accompanying drawings, in which Figure 1 shows a circuitarrangement applicable to two receiving channels of a diversity systemfor carrying out my invention;

Fig. 2 shows an expansion of the system of Fig. 1 to the requirements ofa diversity receiving system having three or more receiving channelsand,

Fig. 3 shows a circuit arrangement for a diversity receiving system inwhich, when the signals are received on different channels in phaseopposition, the energy derived from one antenna will be reversed inphase. This circuit arrangement shows further the technique involved incombining the energies from three or more antennae by reversal ofcertain out-of-phase components whenever they occur in any one or moreof the separate channels.

Referring first to Fig. 1, I show therein two transformers I and 2through which signal energy is fed from separate points of collection.Transformer l feeds to an amplifier tube 3 while transformer 2 feeds toan amplifier tube 4. The outputs from the tubes 3 and 4 combined and fedin parallel to a transformer l5. The secondary of this transformer isconnected to any suitable utilization device.

The signal which is applied to the grid 1 of tube 3 is also appliedthrough a blocking condenser 20 to the grid l3 of amplifier tube 9.Likewise the signal which is applied to the grid 8 of tube 4 is alsoapplied through blocking condenser 2! to the grid l4 of an amplifiertube Ill. The outputs from tubes 9 and in are combined and fed inparallel to transformer l6 which in turn feeds a diode detector tube H.

The rectified voltage developed across a diode resistor [9 produces aneffective shift of the terminal potentials of a direct current biasingsource I8 with respect to ground. The bias potential applied throughresistor l9, source I8, and the secondary of transformer 2 to the grid 8of tube 4 renders this tube conductive so long as the tube ll continuesto rectify signal energies that are in substantial phase agreement.

The output energies from tubes 3 and 4 will, under normally favorableconditions of reception, be additive and maximum power will be deliveredto transformer l5 as a derivative of the two receiving channels.

Under conditions of phase opposition of the energies received on the twochannels, however, it will be seen that a cancellation of energies wouldoccur in the combined output of the tubes 3 and 4 providing their signalstrengths during such time are equal or substantially equal. It,therefore, becomes necessary to out 01f the output from tube 4 and thisis accomplished by shifting the bias applied to the grid 8 in thenegative direction. The bias shift is accomplished by the failure of therectifier tube I! to be fed with sufficient energy from the combinedoutputs of tubes 9 and E to cause an appreciable voltage drop in theresistor IS. The full negative bias voltage from the source H3 is,therefore, applied to the grid 8 in tube 4. This tube is thus blockedand delivers no out-of-ph'ase signals to the transformer I5.

Upon restoration of an in-phase relationship between the signalsrespectively fed to the tubes 9 and I0 from the different channels, therectified energy in the detector tube H produces a voltage drop in theresistor I? which is opposed to the voltage of the biasing source i8.The normal bias is, therefore, restored to the grid 3 of tube 4 and theoutput from this tube is then added to that of tube 3. The phaserelation between the signals in the respective receiving channels is,therefore, the controlling factor in governing the bias on the grid 8 oftube Referring now to Fig. 2, I show how the system of Fig. 1 may beextended to cover the combined action of signal energies derived from asmany as three separate receiving antennae and associated circuits. Theelements in combination, so far as they were shown and described in Fig.1, are duplicated'in this Fig. 2 with the addition of further elementsnow .to be described.

The output energies from tubes 3 and are combined and fed to one side ofthe primary in transformer I5, as before. When tube 4 is blocked thesignal is derived entirely from the output circuit of tube 3. A thirdsource of signal energy may be fed through the transformer 22 to thegrid 33 of tube 25. This tube operates in conjunction with the signal asamplified by tube 25 whose grid 28 receives its control from thesecondary of transformer l5. The anode 21 of tube 25 and the anode 29 oftube '25 are interconnected and both circuits are combined in theprimary winding of transformer 31.

Part of the signal energy derived from transformer I5 is divertedthrough blocking condenser 23 to the grid of a tube 3!. Likewise a partof the signal energy from the secondary of transformer 22 is divertedthrough blocking condenser 24 to the grid 34 of tube 32. Tubes 3| andfunction in exactly the same manner as tubes 9 and H] for the purpose ofdetermining the phase relation between the signals in the twotransformers I5 and 22. When these signals are in phase the resultantoutput energies from tubes 3| and 32 are such as to produce a rectifyingaction in the diode tube 39, energy being fed thereto across thetransformer 38. Rectification of these energies produces a voltage dropin the resistor 40 which is opposed to the normal D. C. bias from thebiasing source'4l applicable to the grid 30 in tube 26. Normally, then,when the signals fed across transformers i5 and 22 are substantially inphase agreement, tube 26 is maintained in the conductive state and itsoutput energy is added to that of tube 25. When, however, phaseopposition occurs, the signals fed to the grids of tubes 3| and 32cancel out and the voltage drop in resistor is reduced to a negligiblevalue. The full voltage of the biasing source 4| is then appliednegatively to the grid 30 of tube 26 thereby blocking the same andpermitting the output energy from the tube 25 to be applied across thetransformer 31 without opposition.

Further diiplications of the circuit arrangements shown in Fig. 2 may,of course, be made as far as may be necessary to extend the comparisonsbetween one set of channels and another. Thus any number of diversitysignal channels may be combined in one utilization circuit.

Referring now to Fig. 3, I show a somewhat different embodiment of theinvention, where, instead of discarding the signals in one of thechannels, the phase of these signals may be reversed and then combinedwith the signalling energy from another channel. This circuitarrangement is described in detail as follows:

Two signals derived from respectively different antennas are fed acrosstransformers 59 and 5|, each of whose secondaries is connectedrespectively to grid 54 in tube 52 and grid 55 in tube 53. The anodes 55and 57 of the tubes 52 and 53 are interconnected and both are connectedto the upper terminal of the primary in a transformer 51. This is apush-pull transformer having the positive terminal of an anode sourceconnected to its center tap. A third tube 58 has its grid 55 controlledacross blocking condenser M by signalling energy from transformer 5| inthe same sense as the control of tube 53. The anode 50 of tube 58,however, is connected to the lower primary terminal of transformer 61.

The signals fed through transformers 5i! and 5| are also used to controlthe grids 53 and 64 respectively in another pair of tubes 6| and 62.These tubes have their anodes 65 and 66 interconnected so that they willfeed in parallel through transformer 68 to a pair of diode detectortubes 69 and i6.

The diode tubes 69 and 76 are so connected as to produce full waverectification of any energies which may be fed thereto acrosstransformer68. The amount of energy rectified, however, depends at all times uponthe .phase relation between the outputs from the tubes 5| and 62. Ifthese outputs are in phase agreement then th amount of energy rectifiedwill be a maxi mum and the voltages developed across the respectivediode resistors H1 and 4! may be utilized in opposite senses as follows:

The negative voltage developed across a resistor 10 connected to theanode of diode tube 69 influences the bias on grid 59 in tube 53 in suchmanner as to block this tube under normal in-phase conditions of thesignals appearing across transformers 5i) and 5|.

Also under normal conditions of phase agreement between the signals fedacross transformers 5E! and 5| the tube 53 is maintained in a conductivestate by virtue of the rectifying action in the diode 15 which producesa positive voltage drop across its resistor 41 connected in oppositionto the normal D. C. biasing source 1|, whose negative terminal isconnected through the secondary of transformer 5| to the grid 55 in tube53.

Consider now the action of tubes BI and '62 and their associatedcircuits including the transformer '68 and the diode tubes 69 and 16when phase opposition occurs between the signalling energies. Theoutputs from tubes 5| and 62 will substantially cancel out, leaving noenergy to be rectified in the tubes 55 and 15. In the absence ofappreciable voltage dropin the two resistors Iii and 4'! tube 58 will berendered conductive while tube 53 will be substantially blocked. This istrue because resistor 70 will no longer deliver a blocking biaspotential to the grid 59 in tube 58 and because, at the same time, theresistor 41 will offer no opposing voltage to that of the D, C. sourceH, in which case this latter source will be fully effective in producinga blocking bias upon the grid 55 in tube 53. Under these conditions ofphase opposition, therefore, tubes 52 and 58 will cooperate, eachdelivering signalling energy to its appropriate one of the opposingterminals of the primary in transformer 61. The signals being in phaseopposition, however, their push-pull combination in the transformer willbe additive.

Fig. 3 also discloses an expansion of the system of combiningphase-opposed signals from two channels so that further combinations ofsignals in and out of phase may be made as when reception is derivedfrom three or more antennas. The same principles of utilizing combiningcircuits are involved as in the case of the embodiment shown in Fig. 2.

Assume now that the signalling energy is collected by three separateantennas feeding respectively to transformers 50, 5| and 15. The outputfrom transformer 15 controls the grid 19 in tube 11 and also (acrosscondenser 98) the grid 83 in tube 82. Tube 11 performs in the samemanner as tube-53, whereas tube 82 fulfills the same function as that oftube 58 but with respect to the signalling energy from a differentantenna.

Likewise the pair of tubes 85, 88 is utilized to compare the phasesbetween the signalling energies derived across transformers 61 and 15respectively. Furthermore, the combining of output energy from tubes 85and 88 in or out of phase renders the diode tubes 93 and 99 more or lessconductive in dependence upon the phase relation of the signals. Thesediodes are arranged to deliver separate half-wave rectificationcomponents of energy induced across transformer 92. The anode of diodetube 93 has associated therewith a resistor 94 and a grid biasingcircuit leading to the grid 83 in tube 82. Also the diode tube 99 hasits cathode connected to a resistor I and also to the positive terminalof a D. C. biasing source 95, the negative terminal whereof is connectedthrough the secondary of transformer 15 to the grid 19 of tube 11. Theanodes 8| and 89 of the respective tubes 11 and 16 are interconnectedand are arranged to feed output energies to the upper terminal of theprimary in transformer 9 I. This transformer is similar to and fulfillscorresponding functions with respect to those of transformer 6'l Whenthe phase of the signals in transformers l and His in agreement, orsubstantially so, then the tubes 16 and T! operate as a team, feedingtheir signalling energy across transformer 9| to the utilization device.At the same time the tubes 85 and 83 operate as a team and their outputenergies are combined and delivered across transformer 92 to the diodetubes 93 and 99. These tubes then fulfill the same functions as diodetubes 69 and 16. That is to say, when the signals are in substantialphase agreement the voltage drop in resistor 94 causes tube 82 to beblocked, while the voltage drop in resistor I09 (opposed to the voltageof the biasing source 95) causes tube 11 to be rendered conductive. Thistube and tube 16 then work together as a team in supplying signallingenergy to the upper terminal of the primary in transformer 9|.

In the case of phase opposition between the signalling energy intransformer 6'! and 15, tube 11 becomes blocked and tube 82 becomesconductive, but since the anode 84 in tube 82 is connected to the lowerterminal of the primary in transformer 91 these phase opposed signalsproduce an additive effect in respect to the signalling energy derivedfrom transformer 67 and amplified by tube 16.

The combining circuits herein shown and described may be used in radiofrequency stages or in intermediate frequency stages, depending upon therequirements of the circuit arrangements.

Various modifications of my invention may be made by those skilled inthe art without departing from the spirit and scope of the inventionitself. The invention is limited, therefore, only in accordance with theclaims.

I claim:

1. In a diversity receiving system, a plurality of receiving circuitseach fed with Wave energy from an appropriate antenna, combining circuitmeans comprising amplifier discharge tubes in-' dividual to eachreceiving circuit and having a common output circuit, means including agrid biasing source operative to maintain a cut-ofi bias on the controlgrid of at least one of said amplifier tubes in the absence ofsubstantial phase agreement between the energies derived from saidreceiving circuits, and means responsive to variations in the phaserelation between the wave energies fed through said receiving circuitsrespectively for deriving a rectified signal energy component which isopposed to said cut-off bias, the two means last recited beingcooperative to render the signal energies of the respective receivingcircuits additive during periods of substantial phase agreement, and tosuppress the amplification of energy in the tube whose control grid isconnected to said biasing source during periods of substantial phaseopposition of the energies in said receiving circuits.

2. In a system according to claim 1, a first pair and a second pair ofamplifier discharge tubes comprised in the first said means, each tubeof the first pair and one of the tubes of the second pair having itscontrol grid connected to a respective one of said receiving circuits,the remaining tube of the second pair having its control grid coupled tothe common output circuit of the first pair, and an additional commonoutput circuit for the second pair.

3. In a system according to claim 1, the elements so defined incombination with amplification means operative only when theamplification of phase-opposed energy is suppressed for delivering auseful component of said energy to said combining circuit means in apush-pull manner.

4. In combination, a plurality of diversity receiving circuits eachindividual to a differently situated antenna, a single amplificationpath in one of said receiving circuits, oppositely phased amplificationpaths in the remainder of said receiving circuits, phase comparisonmeans operative in respect to a pair of said amplification paths, andswitching means operative in dependence upon the instantaneousdeterminations of said phase comparison means whereby one of saidoppositely phased amplification paths is selected to the exclusion ofthe other, and means for combining the energy delivered by the select-,ed amplification path with that delivered by said single amplificationpath.

5. The combination according to claim 4 and including at least three ofsaid receiving circuits,

said phase comparison means comprising different sections eachappropriate to a different group of said receiving circuits.

6. In a diversity receiving system, a pair of diversity receivingcircuits, an amplifier for one of said circuits, two amplifiers for theother of said circuits, an output transformer having one terminal of itsprimary winding connected in common to corresponding output leads fromthe first said amplifier and from one of the other two amplifiers, aconnection from the other primary terminal to the corresponding outputlead from the remaining amplifier, and means operative in dependenceupon variations in the phase relations between the input energiesrespectively fed to the several amplifiers of said receiving circuitsfor causing the output energies thereof to be at all times combined inaiding relation to one another in said transformer.

'7. The combination according to claim 6 wherein the last said meanscomprises a device for amplifying a diverted part of the energy fromeach receiving circuit, means for combining and detecting said divertedenergies, and gain control devices operative as a voltage function ofthe combined and detected energy for enabling one of the two amplifiersfor one receiving circuit to amplify while blocking the other of saidtwo amplifiers.

8. In a diversity receiving system, the device as defined by claim 6 incombination with a third receiving circuit, two amplifiers for saidthird receiving circuit, an amplifier having an input circuit fed withenergy from said output transformer,.a second output transformer havingone terminal of its primary winding connected in common to correspondingoutput leads from the amplifier last mentioned and one of the twoamplifiers of said third receiving circuit, a connection from the otherprimary terminal of said second output transformer to the correspondingoutput lead from the remaining amplifier of said third receivingcircuit, and means operative in dependence upon the phase of the inputenergy fed to the two amplifiers of said third receiving circuit inrelation to the phase of the energy delivered to the first saidtransformer for causing the output energies derived from each of saidamplifiers to be either suppressed or combined in aiding relation to oneanother in said second output transformer.

ROBERT E. SCHOCK.

